Exposure apparatus

ABSTRACT

An exposure apparatus includes an illumination optical system that includes an optical integrator for forming a secondary light source from the light, and a variable stop arranged at or near a position where the secondary light source is formed, the diameter variable stop that defines a NA of the illumination optical system, a projection optical system that includes an aperture stop arranged at a position substantially optically conjugate with the variable stop, the aperture stop defining a numerical aperture of the projection optical system, and a controller for controlling the aperture diameter of the variable stop as the aperture diameter varies so that an image of the secondary light source can fall within the aperture diameter of the aperture stop.

[0001] This application claims the right of priority under 35 U.S.C.§119 based on Japanese Patent Application No. 2003-162044, filed on Jun.6, 2003, which is hereby incorporated by reference herein in itsentirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to an exposure apparatus,and more particularly to an exposure apparatus used to expose objects,such as single crystal substrates for semiconductor wafers and glassplates for liquid crystal displays (“LCD”).

[0003] A reduction projection exposure apparatus has been conventionallyemployed that uses a projection optical system to project or transfer acircuit pattern on a reticle (or a mask) onto a wafer, etc., in order tomanufacture fine semiconductor devices such as a semiconductor memory ora logic circuit in photolithography technology.

[0004] Recent demands for smaller and thinner profile electronic deviceshave increasingly called for finer semiconductor devices to be mountedonto these electronic devices. The exposure apparatus is required tohave such high optical performance as the critical dimension (orresolution) on a wafer surface of 0.2 μm or, preferably, 0.1 μm.

[0005] The semiconductor industry has recently shifted its production toa highly value-added system chip that mixes a wide variety of patternsthe reticles needing plural types of patterns. Reticle patterns includean adjacent and periodic line and space (L & S) pattern, a line ofcontact holes that are adjacent and periodic (i.e., arranged at the sameinterval as the holes diameters), isolated contact holes that arenon-adjacent and isolated, other isolated patterns, etc. A transfer of apattern with high resolution requires a selection of optimal exposureconditions in accordance with these kinds of patterns.

[0006] In order to handle exposure processes of various featuredpatterns, more specifically, to set an exposure condition suitable foreach exposure process, an exposure apparatus has been proposed (forexample, in Japanese Patent Application, Publication No. 5-299321) thatcan change a numerical aperture (“NA”) in the projection optical system,an illumination condition, such as a coherence factor σ (i.e., a ratioof an illumination optical system's NA to a projection optical system'sNA), and a σ distribution in the illumination area (for a so-calledmodified illumination, such as an oblique incidence illumination, amulti-pole illumination, and an off-axis illumination).

[0007] However, when the projection optical system's NA, theillumination optical system's NA and an effective light source shape arechanged independently, the illumination light from the illuminationoptical system can be larger than the projection optical system's NA anddisadvantageously shielded by the projection optical system. As aresult, the imaging performance deteriorates and the light intensitybecomes uneven. In particular, the recently frequently used modifiedillumination among the resolution-enhanced technology (“RET”) has alarge σ value, thus this problem is likely to happen.

[0008] The exposure apparatus proposed in the above reference includes ameans for alarming an error or prohibiting an exposure action when anoperator's setting causes the 0-th order light in illumination light,that passes through an illumination stop and the reticle, not to passthrough the projection optical system. Thus, this reference arduouslyrequires the operator to avoid this problem at the time of the setting.

[0009] In addition, as the off-axis telecentricity is adjusted forcorrections of on-axis and off-axis telecentricity, the outline of the adistribution decenters, the projection optical system can similarlyshield the illumination light, and the imaging performance deteriorates.It is therefore important that the illumination light (in particular,the 0-th order light) enters the projection optical system in view ofits NA even when the a distribution decenters.

BRIEF SUMMARY OF THE INVENTION

[0010] Accordingly, it is an exemplified object of the present inventionto provide an exposure apparatus that prevents shielding of theillumination light and provides excellent imaging performance.

[0011] An exposure apparatus of one aspect according to the presentinvention includes an illumination optical system for illuminating areticle using light from a light source, wherein the illuminationoptical system includes an optical integrator for forming a secondarylight source from the light, and a variable stop arranged at or near aposition where the secondary light source is formed, the variable stopbeing configured to vary an aperture diameter that defines a numericalaperture of the illumination optical system, a projection optical systemfor projecting a pattern on the reticle onto an object to be exposed,wherein the projection optical system includes an aperture stop arrangedat a position substantially optically conjugate with the variable stop,the aperture stop defining a numerical aperture of the projectionoptical system, and a controller for controlling the aperture diameterof the variable stop in the illumination optical system as the aperturediameter of the variable stop varies so that an image of the secondarylight source formed at or near the aperture stop can fall within theaperture diameter of the aperture stop.

[0012] An illumination apparatus of another aspect according to thepresent invention for illuminating a surface using light from a lightsource includes a condenser optical system that includes at least twogroups of optical systems for introducing the light into the surface,wherein the condenser optical system makes a focal length and a backprincipal point position of the condenser optical system substantiallyconstant, while making a front principal point position of the condenseroptical system variable.

[0013] An illumination apparatus of still another aspect according tothe present invention for illuminating a surface using light from alight source includes an optical integrator for forming a secondarylight source from the light, and a condenser optical system thatintroduces the light from the optical integrator into the surface, andincludes at least two groups of optical systems, wherein the condenseroptical system makes a focal length and a back principal point positionof the condenser optical system substantially constant, while making afront principal point position of the condenser optical system variable.

[0014] An illumination apparatus of still another aspect according tothe present invention for illuminating a surface using light from alight source includes a zooming optical system for introducing the lightto an optical integrator and for adjusting a size of a secondary lightsource formed by the optical integrator, and a condenser optical systemthat introduces the light from the optical integrator to the surface tobe illuminated, and includes at least two or more optical elements,wherein the zooming optical system adjusts the size of the secondarylight source in accordance with an adjustment of an interval between theoptical elements that constitute the condenser optical system.

[0015] An exposure apparatus of another aspect according to the presentinvention includes the above illumination optical system, and aprojection optical system for projecting a pattern on a reticleilluminated by the illumination optical system, onto an object to beexposed.

[0016] A device fabricating method of still another aspect of thepresent invention includes the steps of exposing an object using theabove exposure apparatus, and performing a predetermined process for theexposed object. Claims for a device fabricating method that performsoperations similar to that of the above exposure apparatus cover devicesas intermediate and final products. Such devices include semiconductorchips like an LSI and VLSI, CCDs, LCDs, magnetic sensors, thin filmmagnetic heads, and the like.

[0017] Other objects and further features of the present invention willbecome readily apparent from the following description of the preferredembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic structural view of an exposure apparatus ofone embodiment according to the present invention.

[0019]FIG. 2 is a schematic view showing an exemplary relationshipbetween the light intensity distribution on the incident surface andthat on the exist surface of a fly-eye lens shown in FIG. 1.

[0020]FIG. 3 is an enlarged view of a principal part in an illuminationoptical system in the exposure apparatus shown in FIG. 1.

[0021]FIG. 4 is a schematic sectional view of a ray shape in a variablestop in the illumination optical system shown in FIG. 1.

[0022]FIG. 5A to 5C are schematic plane views of various aperture stopsapplicable to the shaping means shown in FIG. 1.

[0023]FIG. 6 is a schematic view showing a relationship between thelight incident upon the fly-eye lens shown in FIG. 1 and the illuminatedsurface.

[0024]FIG. 7 schematically shows effective light source distributions atrespective image points on the illuminated surface when a ray having thelight intensity distribution shown in FIG. 2 enters the fly-eye lensshown in FIG. 1.

[0025]FIG. 8 schematically shows effective light-source distributions atrespective image points on the illuminated surface when a ray having thelight intensity distribution shown in FIG. 2 enters the fly-eye lensshown in FIG. 1 and the telecentricity of the effective light sourcedistribution is corrected.

[0026]FIG. 9 is a schematic view of an image of a variable stop in theillumination optical system on the aperture stop in the projectionoptical system shown in FIG. 1.

[0027]FIG. 10 is an enlarged view of a principal part of theillumination optical system in the exposure apparatus shown in FIG. 1.

[0028]FIG. 11 is a flowchart of an exposure method according to oneaspect of the present invention.

[0029]FIG. 12 is a flowchart for explaining how to fabricate devices(like semiconductor chips such as ICs and LCDs, CCDs, and the like).

[0030]FIG. 13 is a detailed flowchart of the wafer process shown in Step4 of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring now to the accompanying drawings, a description will begiven of an exposure apparatus 1 according to the present invention.Each element in each figure is designated by the same reference numeral,and a duplicate description will be omitted. FIG. 1 is a schematicstructural view of the exposure apparatus 1. The exposure apparatus 1includes, as shown in FIG. 1, an illumination apparatus 100, a reticle200, a projection optical system 300, a plate 400, and a controller 500.The exposure apparatus 1 is a projection exposure apparatus that exposesonto the plate 500 a circuit pattern created on the reticle 200, forexample, by a step-and-repeat or by a step-and-scan manner.

[0032] The illumination apparatus 100 illuminates the reticle 200, andincludes a light source section 110 and an illumination optical system120.

[0033] The light source section 110 employs, for example, lasers such asan ArF excimer laser with a wavelength of approximately 193 nm, or a KrFexcimer laser with a wavelength of approximately 248 nm, etc., but thetype of laser is not limited to an excimer laser, and an F₂ excimerlaser with a wavelength of approximately 157 nm can be used. The numberof light sources is also not limited. When the light source section 110uses a laser, it is desirable to employ a beam shaping optical systemthat shapes a parallel beam from a laser source to a desired beam shape,and an incoherently turning optical system that turns a coherent laserbeam into an incoherent one. A light source applicable to the lightsource section 110 is not limited to the laser, but may use one or morelamps such as a mercury lamp, xenon lamp, etc.

[0034] The illumination optical system 120 is an optical system forilluminating the reticle 200, and includes a lens, a mirror, an opticalintegrator, a stop, etc. The illumination optical system of the instantembodiment includes a uniform ray forming means 121, a shaping means122, a zooming (or imaging) optical system 123 a to 123 c, a fly-eyelens 124, a variable stop 125, a condenser optical system 126, a maskingblade 127, and imaging optical systems 128 and 128 b. A detaileddescription of the illumination optical system will be given later.

[0035] The reticle 200 is made from quartz, for example, and forms acircuit pattern (or an image) to be transferred, and is supported anddriven by a reticle stage (not shown). Diffracted light emitted from thereticle 200 passes through the projection optical system 300, and thenis projected onto the plate 400. The reticle 200 and the plate 400 arelocated in an optically conjugate relationship. The exposure apparatus 1of the instant embodiment is a scanner, and the reticle 200 and theplate 400 are scanned at a speed ratio corresponding to a reductionratio to transfer the pattern on the reticle 200 onto the plate 400. Ifit is a step-and-repeat exposure apparatus (referred to as a “stepper”),the reticle 200 and the plate 400 remain still for the exposure.

[0036] The projection optical system 300 is an optical system forprojecting light that reflects the pattern on the reticle 200 onto theplate 400. The projection optical system 300 has an aperture stop 310that defines an arbitrary NA. The aperture stop 310 has a variableaperture diameter that defines the NA of an imaging ray on the plate400, and varies the aperture diameter to adjust the NA if necessary. Inthe instant embodiment, a is a ratio between the diameter of an image ofeach light source formed by a fly-eye lens 124 at a position of theaperture stop 310 and the aperture diameter of the aperture stop 310.

[0037] The projection optical system 300 of the instant embodiment is anoptical system that includes only plural lens elements 320 a and 320 b,but may also be a catadioptric optical system comprised of a pluralityof lens elements with at least one concave mirror, an optical systemcomprised of a plurality of lens elements and at least one diffractionoptical element such as a kinoform, a catoptric optical system includingonly mirrors, and so on. Any necessary correction of a chromaticaberration in the projection optical system 300 can use a plurality oflens units made from glass materials having different dispersion values(Abbe values), or arrange a diffraction optical element such that itdisperses in a direction opposite to that of the lens unit.

[0038] The plate 400 is a wafer in the instant embodiment, but mayinclude a liquid crystal plate and a wide range of other objects to beexposed. A photoresist is applied onto the plate 400.

[0039] The plate 400 is supported by the plate stage 450. The platestage 450 may use any structure known in the art, and a detaileddescription of its structure and operations is omitted. For example, theplate stage 450 uses a linear motor to move the plate 400 in X-Ydirections. The reticle 200 and plate 400 are, for example, scannedsynchronously, and the positions of the reticle stage (not shown) andplate stage 450 are monitored, for example, by a laser interferometerand the like, so that both are driven at a constant speed ratio. Theplate stage 450 is installed on a surface plate stool supported on thefloor and the like, for example, via a dumper, while the reticle stage(not shown) and the projection optical system 300 are installed on abarrel surface (not shown) supported by the base frame placed on thefloor, for example, via a dumper.

[0040] The controller 500 includes a CPU (not shown) and a memory (notshown), and controls the actions of the exposure apparatus 1. Thecontroller 500 is electrically connected to the illumination apparatus100, the reticle stage (not shown), the projection optical system 300,and the plate stage 450. The controller 500 controls the aperturediameter of a variable stop 125 in the illumination optical system 120so that an image from the secondary light source, formed by the fly-eyelens 124 at a position of the aperture stop 310 in the projectionoptical system 300, falls within the aperture diameter of the aperturestop 310. The controller 500 controls the aperture diameter of thevariable stop 125 in the illumination optical system 120 so thatσ≦(x−1)/x where x is the number of fine lenses in the fly-eye lens 124corresponding to σ=1. The fly-eye lens 124 serves as an opticalintegrator and generally includes twenty or more optical elements (suchas fine lenses). The controller 500 controls the ratio between theillumination optical system 120's NA and the projection optical system300's NA so that (the illumination optical system 120's NA)/(theprojection optical system 300's NA) is less than or equal to, forexample, 0.95. The controller 500 may serve as an adjuster 600, whichwill be described later.

[0041] A description will now be given of the illumination opticalsystem 120, with reference to FIGS. 2 to 10. The light emitted from thelight source section 110 that has an excimer laser, etc., is convertedinto an approximately uniform light distribution on a predeterminedsurface A by a uniform ray forming means 121. The uniform ray formingmeans 121 includes at least one of the following: a fly-eye lens, anoptical pipe that uses internal reflections, a diffraction grating,etc., or a combination thereof, such as a plurality of opticalintegrators, a relay optical system, a condenser optical system, amirror, etc. The uniform ray forming means 121 varies light from thelight source section 110 into a desired uniform light distribution onthe predetermined surface A. The predetermined surface A may arrange astop having a circular or octagonal shape to limit the lightdistribution into a XY symmetrical distribution.

[0042] A shaping means 122 makes the center part of the secondary lightsource formed by the fly-eye lens darker than the peripheral part, andis removably located near the predetermined surface A.

[0043] The shaping means 122 can use a conical optical element 122 a, aninterval variable conical optical element 122 b, a properly shaped stop,such as a quadrupole aperture stop 122 c shown in FIG. 5A, a dipoleaperture stop 122 d shown in FIG. 5B, and an annular aperture stop 122 eshown in FIG. 5C, a parallel plate (not shown), a pyramidal opticalelement (not shown), a triangle pole shaped optical element (not shown),a variable stop that can change a shape and/or a diameter, a filterhaving a proper transmittance distribution, or a modification-variableenlargement/reduction beam expander.

[0044] The shaping means 122 can arrange some of these elements on theoptical axis at the same time.

[0045] The conical optical element 122 a has a concave conical incidentsurface, and a convex conical exit surface, and serves to form anannular ray when located along the optical axis.

[0046] The conical optical element 122 b includes an optical element OM₁that has a concave conical incident surface and a flat exit surface, anda pyramidal optical element OM₂ that has a flat incident surface and aconvex conical exit surface. The conical optical element 122 b whenlocated along the optical axis forms an annular ray. The adjusting of aninterval between the optical elements OM₁ and OM₂ can change the size ofthe annulus (or an annular ratio). Such a structure of the conicaloptical element 122 b can efficiently form the annular ray in a smallspace. The optical elements OM₁ and OM₂ have approximately the sameconical surface angle. The same angle would reduce the angle of the exitlight from the shaping means 122, and minimize the shielding of light bythe subsequent optical systems. When the subsequent optical system hasangular latitude, these angles are not necessarily made the same, butmay be different, for example, in order to reduce an annular width.

[0047] Similar to the conical optical element 122 b, is an intervalvariable quadrupole conversion element that has an incident side opticalelement with a concave pyramidal incident surface and an exit sideoptical element with a convex pyramidal surface. A triangle pole shaped,dipole conversion element is also applicable. The shaping means 122 usessuch a proper transmission optical element and can convert a ray shapeinto one in which the peripheral part has a larger light intensitydistribution than that of the central part.

[0048]FIG. 5A is a schematic plane view of the quadrupole aperture stop122 c that has a light shielding part LT, and quadrupole lighttransmitting parts TM, each having a circular opening with atransmittance of 1. The transmitting parts TM are arranged at ±45° and±135°. Preferably, each transmitting part TM provides the same σ to theillumination light. The transmitting parts TM can be formed indirections of 0°, 90°, 180° and 270° or have different sizes accordingto patterns on the reticle 200. The transmitting part TM may have suchvarious shapes as a rectangle, another polygon, or part of a sector.FIG. 5B is a schematic sectional view of the dipole aperture stop 122 dhaving a light shielding part LT and dipole light transmitting parts TMhaving circular openings with a transmittance of 1. FIG. 5C is aschematic plane view of an annular aperture stop 122 e having a lightshielding part LT and a light transmitting part TM having an annularopening with a transmittance of 1.

[0049] A magnification-variable zooming optical system (123 a to 123 c)varies a magnification of the circular shaped ray formed on thepredetermined surface A or the ray that has been desirably shaped by theshaping means 122. The circularly or desirably shaped ray enters theincident surface of the fly-eye lens 124 that serves as the opticalintegrator.

[0050] The fly-eye lens 124 serves as the optical integrator, and formsa plurality of light source images or secondary light sources near theexit surface of the fly-eye lens 124 from the incident light. Thevariable stop 125 is provided near the surface, on which the plurallight source images are formed. The variable stop 125 is located at aposition that slightly defocuses (by ± several millimeters) from thesurface, on which the plural light source images are formed (or a backfocal surface of the fine lenses that form the fly-eye lenses) becausethe surface has a comparatively high energy density of light. When thevariable stop 125 endures the energy density, the variable stop 125 canbe located on the surface, on which the plural light source images areformed.

[0051] The variable stop 125 can vary an aperture diameter that definesthe illumination optical system 120's NA. The aperture diameter isvaried according to the projection optical system 300's NA, as discussedlater. The variable stop 125 and the aperture stop 310 are arranged in asubstantially optically conjugate relationship. The fly-eye lens 124forms multiple light sources at the exit surface side of the variablestop 125, and their images formed at the position of the aperture stop310 provide a shape of the illumination ray (or an effective lightsource shape) at respective points on the plate 400 surface. Themultiple light sources formed by the fly-eye lens 124 are not restrictedby the variable stop 125, and are referred to as “secondary lightsources” hereinafter.

[0052] Among rays from the multiple light source images, rays that arenot restricted by the variable stop 125 illuminate the masking blade127's surface via the condenser optical systems 126 a and 126 b. Themasking blade 127 is arranged, via the imaging optical systems 128 a and128 b, at a surface substantially optically conjugate with the surfacewhere the reticle 200 is arranged. The masking blade 127 defines anilluminated area on the reticle 200's surface.

[0053] When the images of the secondary light sources at the aperturestop 310 position in the projection optical system 300 are larger thanthe aperture stop 310, the direct light that has transmitted through theillumination optical system 120 (or the 0-th order light from thereticle 200) is shielded by (the light shielding part on) the aperturestop 310 in the projection optical system 300. As a result, asdiscussed, is that the imaging performance deteriorates and the lightintensity becomes uneven, negatively affecting the semiconductor devicemanufacture.

[0054] Accordingly, the inventive exposure apparatus 1 uses thecontroller 500 to control the aperture diameter of the variable stop 125in the illumination optical system 120 as the projection optical system300's NA varies, so that the 0-th order light from the reticle 200,which has passed through the variable stop 125 in the illuminationoptical system 120, falls within the aperture diameter in the aperturestop 310 in the projection optical system 300. In other words, thecontroller 500 controls the illumination optical system 120's NA so thatthe 0-th order light from the reticle 200 is not shielded by theaperture stop 310 in the projection optical system 300.

[0055]FIG. 2 is a schematic view showing an exemplary relationshipbetween a light intensity distribution on the incident surface and thaton the exist surface of the fly-eye lens 124 shown in FIG. 1. However,strictly speaking, FIG. 2 exemplarily shows a relationship between alight intensity distribution on the incident surface of the fly-eye lens124 and that of the secondary light sources formed near the variablestop 125.

[0056] In FIG. 2, D₀ is an exemplary light intensity distribution on theincident surface of the fly-eye lens 124, and E is an exemplarysecondary light source. The light source distribution of light emittedfrom the light source section 110 is converted into a discretedistribution corresponding to the fine lenses in the fly-eye lens 124when the light passes through the fly-eye lens 124. The peak outline E₀that connects peak values of the discrete distribution has approximatelythe same shape as that of the light intensity distribution D₀ for theaperture diameter of the variable stop 125 in the illumination opticalsystem 120. Substantially, the light intensity distribution D₀ and theaperture diameter of the variable stop 125 determine a shape of thesecondary light source.

[0057]FIG. 3 is an enlarged view of a principal part in an exemplaryillumination optical system 120 in the exposure apparatus 1 shown inFIG. 1. FIG. 4 is a schematic sectional view showing a ray shape in avariable stop 125 in the illumination optical system 120 shown in FIG.1.

[0058]FIG. 3A shows so-called normal illumination where the shapingmeans 122 is retreated from the optical path or where a circular stop ora parallel plate is arranged near the predetermined surface A. Asillustrated, the uniform ray forming means 121 forms a substantiallycircular shaped ray with a uniform light intensity distribution on thepredetermined surface A. Due to the uniform ray forming means 121, raysfrom plural angles overlap each other and form a uniform light intensitydistribution on the predetermined surface A; even when the light sourcesection 110 uses a light source having strong directivity such as alaser, the light can maintain a certain NA as shown by an arrow in FIG.3A.

[0059] The magnification-variable zooming optical system (123 a-123 c)projects the light intensity distribution on the predetermined surface Aonto the incident surface of the fly-eye lens 124 at a predeterminedmagnification. The light intensity distribution when imaging on theincident surface of the fly-eye lens 124 without aberration wouldexhibit a sharp outline, and causes uneven light intensity and uneveneffective light source on the screen of the plate 400 that serves as anexposed surface. Therefore, imaging between the predetermined surface Aand the incident surface of the fly-eye lens 124 preferably needsaberration (including defocusing) to some extent. This is not true whenthe fly-eye lens 124 includes many fine lenses and the influence on theuneven light intensity, etc. is small. Blurs corresponding to about oneor more fine lenses are usually preferable. FIG. 4D is a sectional viewof a light intensity distribution F₄ in such a state.

[0060] As described with reference to FIG. 2, the light intensitydistribution of the fly-eye lens 124 substantially determines the shapeof the secondary light source (or an effective light source). In FIG.3A, the secondary light source is small enough for the variable stop 125in the illumination optical system 120. In order to change a σ value(effective σ value that considers the distribution), themagnification-variable zooming optical system (123 a to 123 b) varies amagnification as shown in FIG. 3B. While the instant embodiment variesthe σ value by changing an interval between the optical systems 123 aand 123 b, any other configuration can be available as long as themagnification becomes variable. A zooming optical system thatapproximately maintains the telecentricity at the exit side of the lightis preferable when the magnification changes (so that the light incidentupon the fly-eye lens does not exceed a certain incident angle after themagnification is changed). When the zooming optical system (123 a-123 c)has a small magnification variable range, the shaping means 122 canemploy the (enlargement/reduction) beam expander and a stop having asmall opening diameter. FIG. 4E shows a large σ value that forms a lightintensity distribution F₅ slightly larger than the aperture diameter inthe variable stop 125 in the illumination optical system 120, and thelight that exceeds the aperture diameter in the variable stop 125 isshielded as unnecessary light. Such a configuration effectively switchesthe normal illumination between about σ=0.1 to about σ=0.9.

[0061] The exposure apparatus 1 allows the controller 500 toautomatically vary the aperture diameter in the variable stop 125 in theillumination optical system 120 in accordance with the set NA in theprojection optical system 300. The controller 500 sets the aperturediameter of the variable stop 125 so that its mechanical size is a fixedvalue that satisfies that σ is about 0.95 or smaller for the projectionoptical system 300's NA. Alternatively, the fixed value itself can bechanged.

[0062]FIG. 3C shows the illumination optical system 120 for the annularillumination. The conical optical element 122 a and annular aperturestop 122 c convert a circular light intensity distribution formed on thepredetermined surface A into an annular shape, and the annular lightintensity distribution is projected onto the incident surface of thefly-eye lens 124 at a proper magnification for so-called annularillumination. In this case, the controller 500 automatically sets theaperture diameter of the variable stop 125 in the illumination opticalsystem 120 in accordance with the projection optical system 300's NA sothat its mechanical size is a fixed value that satisfies that σ is about0.95 or smaller.

[0063]FIG. 4A shows a relationship between the variable stop 125 in theillumination optical system 120 for the annular illumination and thesecondary light source (or effective light source). Referring to FIG.4A, the annular light intensity distribution F₁ is formed within theaperture diameter in the variable stop 125. FIG. 4B shows a sectionallight intensity distribution F₂ that is a section of the annular lightintensity distribution F₁ shown in FIG. 4A in an X direction.

[0064] In the case of the annular illumination, the sectional lightintensity distribution F₂ is usually defined as a flat distribution, asshown in FIG. 4B. However, it is difficult to effectively form the flatsectional light intensity distribution F₂, and a pursuit of efficiencywould result in the sectional light intensity distribution F₃ having auneven distribution as shown in FIG. 4C. As a result of a simulation,etc. of the imaging performance, the sectional light intensitydistribution F₃ is selected for performance purposes, which isapproximately equivalent to the sectional light intensity distributionF₂ shown in FIG. 4B.

[0065] The annular illumination is often used to image fine patterns.The effective outer σ, which is the size outside the annular shape whenthe imaging performance is converted into the flat sectional lightintensity distribution F₂ shown in FIG. 4B, often uses about 0.9 for theannular illumination. In this case, as shown in FIG. 4C, the small partthat is located outside the sectional light intensity distribution F₂has a σ of 0.95 or greater, possibly deviating the light from theaperture diameter in the aperture stop 310 in the projection opticalsystem 300. Therefore, the exposure apparatus 1 allows the controller500 to control the size of the aperture diameter in the variable stop125 in the illumination optical system 120 in accordance with theprojection optical system 300's NA while maintaining σ to be about 0.95,and adjusting the light intensity distribution to provide the desiredannular illumination.

[0066] As discussed, the inventive exposure apparatus 1 automaticallyvaries the illumination optical system 120's NA according to the set NAof the projection optical system 300, facilitating the operator'smanipulations. A stop in an illumination optical system in aconventional exposure apparatus determines an effective light source,whereas the variable stop 125 in the illumination optical system 120 issupplemental, and an optical system prior to the fly-eye lens 124substantially defines an effective light source in the inventiveexposure apparatus 1. Therefore, the aperture diameter in the variablestop 125 in the illumination optical system 120 can be uniquelydetermined according to the projection optical system 300's NA.

[0067] A description will now be given of the reason why the aperturediameter of the variable stop 125 in the illumination optical system 120is set so that σ is less than or equal to 0.95 rather than σ=1. FIG. 6is a schematic view showing a relationship between the light incidentupon the fly-eye lens 124 shown in FIG. 1 and an illumined surface C.The illuminated surface C is an optically conjugate surface such as themasking blade 127 surface or the reticle 200 surface, with the surfaceof an object to be exposed (the plate 400 surface).

[0068] Rays L₁, L₂ and L₃ incident upon the center fine lens MLa amongthe fine lenses ML that form the fly-eye lens 124 form one light sourceimage SI due to the fine lens MLa, and Koehler-illuminates theilluminated surface C via the condenser optical system 126. The lightsource image SI is located at the center of the opening of the variablestop 125, and rays L₁′, L₂′ and L₃′ from the light source image SIconstitute principal rays at respective image points C₁ to C₃. FIG. 6shows a telecentric system on the illuminated surface C, and shows thatwhen the effective light source is telecentric at respective imagepoints C₁ to C₃ on the illuminated surface C, the illumination light istelecentric on the plate 400's surface as the object surface to beexpected.

[0069] The telecentricity of the plate 400's surface is an importantfactor for the imaging performance. Non-telecentricity leads to anasymmetrical image.

[0070]FIG. 7 is a schematic view of an effective light sourcedistribution at respective image points on the illuminated surface Cwhen the light intensity distribution D₀ shown in FIG. 2 enters thefly-eye lens 124 shown in FIG. 1. Referring to FIG. 7, the effectivelight source distribution D₁ at the image point C₁ on the illuminatedsurface C, is similar to the position P₁ on the light intensitydistribution D₀ whose principal ray enters the fly-eye lens 124, andmaintains the telecentricity. The effective light-source distribution D₂at the image point C₂ at the outermost axis on the illuminated surface Cis a distribution corresponding to the light intensity distribution D₀at the position P₂ whose principal ray enters the fly-eye lens 124.Therefore, the image point C₂ of the illuminated surface C provides theeffective light-source distribution D₂ that has the telecentricityoffset by a half-pitch of the fine lens MLa that forms the fly-eye lens124.

[0071] Light that has a flat sectional light intensity distribution andilluminates an area much larger than the aperture diameter in thevariable stop 125 in the illumination optical system 120 also providesthe effective light-source distribution that has the telecentricityoffset by a half-pitch of the fine lens MLa. This is not a matterbecause the flat sectional light intensity distribution is maintainedeven when the telecentricity is offset by a half-pitch. In other words,a problem arises when light that has an unflat sectional light intensitydistribution illuminates an area smaller than the aperture diameter inthe variable stop 125 in the illumination optical system 120.

[0072]FIG. 8 schematically shows that the light having the lightintensity distribution D₀ shown in FIG. 2 enters the fly-eye lens 124shown in FIG. 1 and the telecentricity of the effective light sourcedistribution is corrected at each image point on the illuminated surfaceC. FIG. 8 corrects the inclination of the principal ray (that passesthrough the center of the variable stop 125) at the image point C₂ atthe outermost axis of the illuminated surface C in order to correct thetelecentricity of the illuminated surface C. Although the inclinedprincipal ray loses the telecentricity, a correction to maintain thetelecentricity is available for the effective light source distributionD₂ at the image point C₂.

[0073] The condenser optical system 126 has an adjuster 600 to correcttelecentricity. The adjuster 600 serves to vary an interval amongoptical elements (such as lenses) in the condenser optical system 126that includes at least two groups of optical systems, and change onlythe front principal point position of the condenser optical system 126while hardly changing the focal distance of the condenser optical system126 and the back principal point position of the condenser opticalsystem 126. In other words, when the adjuster 600 moves, in anoptical-axis direction, a position of an image of the variable stop 125in the illumination optical system 120, which is formed near theaperture stop 310 in the projection optical system 300, thetelecentricity of the effective light source is corrected at respectiveimage points. The above system can be realized, for example, by anafocal optical system that has a non-equimultiple magnification andexits approximately parallel light in response to incident parallellight that is set to a front group in the condenser optical system 126,and a position of the front group is made variable in the optical-axisdirection.

[0074] The light intensity distributions have various telecentricoffsets on the incident surface of the fly-eye lens 124, and theadjuster 600 varies a principal point position of the condenser opticalsystem 126 to provide optimal telecentricity, and changes the effectivelight source shape.

[0075] When the focal distance of the condenser optical system 126slightly changes as the principal point position of the condenseroptical system 126 changes and the size of the effective light source onthe illuminated surface C consequently changes, a fine adjustment isperformed by the magnification of the zooming optical system (123 a to123 c).

[0076] When the condenser optical system 126 and the adjuster 600 thusvary inclinations at respective image points C₁ to C₃ of light thatpasses through the center of the variable stop 125 in the illuminationoptical system 120, an image of the variable stop 125 at the aperturestop 310 position in the projection optical system 300 is formed, asshown in FIG. 9, so that an image D₁A of the light that passes throughthe center of the center image point C₁ is formed at an apertureposition in the aperture stop 310, and an image D₂A of the light thatpasses through the center of the image point C₂ as the outermost axisdecenters from the center of an aperture position in the aperture stop310. Therefore, when a diameter of the image D₁A is set to 1, relativeto the aperture diameter of the aperture stop 310 in the projectionoptical system 300 (or where the mechanical σ=1 in the variable stop125), the image D₁A projects outside the aperture diameter of theaperture stop 310. Here, FIG. 9 is a schematic view of an image of thevariable stop 125 in the illumination optical system 120 at the aperturestop 310 in the projection optical system 300 shown in FIG. 1.

[0077] Other factors should be considered, such as scattering sizes anddistortions of respective image points and telecentric adjustmentmargins, the diameter of the image D₁A preferably being limited to about95% of the aperture stop 310 (or the σ of the geometric shape of thevariable stop 125 being 0.95). When the number of fine lenses is smallin the fly-eye lens 124 or when the set precision is bad, a small σ ispreferable. Here, the scattering sizes and distortions of respectiveimage points result from a decentered optical arrangement between thevariable stop 125 in the illumination optical system 120 and theaperture stop 310 in the projection optical system 300, their setprecisions, and the aberration of the optical system 126. Thetelecentric adjustment is necessitated as a result of uneven coating anderrors in the optical system.

[0078]FIG. 10 is an enlarged view of a principal part of theillumination optical system 120 in the exposure apparatus 1 shown inFIG. 1. This figure shows an example where the variable stop 125 in theillumination optical system 120 is used to change the effective lightsource distribution rather than for supplemental use. The shaping means122 (which is the conical optical element 122 a in the instantembodiment) forms a ray having a light intensity distribution with apredetermined annular ratio (e.g., a ½ annulus). The zooming opticalsystem (123 a to 123 c) then properly changes a magnification of the rayhaving the predetermined annular ratio, and the ray then enters theincident surface of the fly-eye lens 124, forming secondary lightsources having the predetermined annular ratio near the exit surface ofthe fly-eye lens 124. The outside of the light intensity distributionsof the multiple light sources is appropriately restricted by changingthe aperture diameter of the variable stop 125. Changes of themagnification of the zooming optical system (123 a to 123 c) and theaperture diameter of the variable stop 125 can form an effective lightsource having such a desired size as a large annular ratio (such as ⅔and ¾ annuluses) irrespective of the annular ratio formed by the shapingmeans 122.

[0079] When the shaping means 122 uses the conical optical element 122 bthe annular ratio can be varied by changing the interval between theoptical elements OM₁ and OM₂. However, the fly-eye lens 124 isrestricted in its incident angle, and when the incident angle exceeds acertain angle, the ray becomes unnecessary, deforms the effective lightsource, and generates uneven light intensity. Therefore, the incidentangle of the light upon the fly-eye lens 124 should be at a certainangle or smaller.

[0080] The nature of the light satisfies Ar×Ad≦Br×Bd, where Ar is theradius of the ray shape on the predetermined surface A, Ad is the ray'sNA on the predetermined surface A, Br is the radius of the ray on theincident surface of the fly-eye lens 124 or the width of an annulardistribution, and Bd is the ray's NA on the incident surface of thefly-eye lens 124. Therefore, when the annular distribution has a smallwidth Br, the ray's NA on the incident surface on the fly-eye lens 124can exceed the incident angle limit of the fly-eye lens 124.

[0081] Therefore, even when the shaping means 122, such as the conicaloptical element 122 b, is used, the annular ratio cannot freely be madelarge. Therefore, the annular ratio can be effectively changed bysetting the interval between the optical elements OM₁ and OM₂ and themagnification of the zooming optical system (123 a to 123 c) in theabove restricted range of the incident angle upon the fly-eye lens 124,and by changing the aperture diameter of the variable stop 125 in theillumination optical system 120 to reduce the outer diameter.

[0082] This is not limited to the annular illumination, but isapplicable to the quadrupole illumination and dipole illumination. Aneffective light source having a desired shape (or a modifiedillumination) is formed when the shaping means 122 converts a ray into adesired size (one in which a center part has a lower light intensitydistribution than that of the peripheral part), and the variable stop125 in the illumination optical system 120 restricts an outer diameterof the light intensity distribution of a secondary light source formedon the exit surface of the fly-eye lens 124. Even in this case, thecontroller 500 controls relative to the set NA of the projection opticalsystem 300 so that the variable stop 125 in the illumination opticalsystem 120 has a geometric σ of 0.95 or smaller.

[0083] A description will be given of an exposure method using theexposure apparatus 1 with reference to FIG. 11. FIG. 11 is a flowchartfor explaining the exposure method 1000 as one aspect according to thepresent invention.

[0084] First, an operator sets the projection optical system 300's NAaccording to the circuit pattern to be transferred onto the plate 400(or a necessary resolution) (step 1002). The operator can arbitrarilyset the projection optical system 300's NA, and the controller 500changes the aperture diameter of the aperture stop 310 in the projectionoptical system 300 to adjust the projection optical system 300's NA tothe set NA.

[0085] The controller 500 calculates the illumination optical system120's NA suitable for the set NA of the projection optical system 300 sothat the 0-th order light from the pattern on the reticle 200 fallswithin the set NA's aperture in the projection optical system 300, morespecifically, the illumination optical system 120's NA/the projectionoptical system 300's NA≦0.95 (step 1004).

[0086] Next, the illumination optical system 120's NA is changed to theNA that was calculated in step 1004 (step 1006). This is done bychanging the aperture diameter in the variable stop 125 in theillumination optical system 120 to the set illumination optical system120's NA to a setting most suitable for the projection optical system300's NA.

[0087] In exposure, light emitted from the light source section 110, forexample, Koehler-illuminates the reticle 200 through the illuminationoptical system 120. The light that has passed and reflects the reticlepattern forms an image on the plate 400 through the projection opticalsystem 300. The exposure apparatus 1 appropriately sets a ratio betweenthe illumination optical system 120's NA and the projection opticalsystem 300's NA, and provides excellent devices (such as semiconductordevices, LCD devices, image pick-up devices (such as CCDs), and thinfilm magnetic heads) with high throughput and economical efficiency.Once the projection optical system 300's NA is set, the controller 500automatically sets the illumination optical system 120's NA. Therefore,the operator runs the exposure apparatus 1 more easily than aconventional one.

[0088] Referring now to FIGS. 12 and 13, a description will be given ofan embodiment of a device fabricating method using the above exposureapparatus 1. FIG. 12 is a flowchart for explaining the fabrication ofdevices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs,etc.). Here, as an example, a description will be given of thefabrication of a semiconductor chip as an example. Step 1 (circuitdesign) designs a semiconductor device circuit. Step 2 (reticlefabrication) forms a reticle having a designed circuit pattern. Step 3(wafer preparation) manufactures a wafer using materials such assilicon. Step 4 (wafer process), which is referred to as a pretreatment,forms actual circuitry on the wafer through photolithography using thereticle and wafer. Step 5 (assembly), which is also referred to as aposttreatment, forms into a semiconductor chip the wafer formed in Step4 and includes an assembly step (e.g., dicing, bonding), a packagingstep (chip sealing), and the like. Step 6 (inspection) performs varioustests for the semiconductor device made in Step 5, such as a validitytest and a durability test. Through these steps, a semiconductor deviceis finished and shipped (Step 7).

[0089]FIG. 13 is a detailed flowchart of the wafer process in Step 4.Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ions into the wafer. Step 15 (resistprocess) applies a photosensitive material onto the wafer. Step 16(exposure) uses the exposure apparatus 200 to expose a circuit patternon the reticle onto the wafer. Step 17 (development) develops theexposed wafer. Step 18 (etching) etches parts other than a developedresist image. Step 19 (resist stripping) removes disused resist afteretching. These steps are repeated, and multilayer circuit patterns areformed on the wafer. The device fabrication method of this embodimentmay manufacture higher quality devices than a conventional one. Thus,the device fabrication method that uses the exposure apparatus 1 anddevices such as resultant products constitute one aspect of the presentinvention.

[0090] Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the scope of the present invention. For example,the inventive exposure apparatus can use an optical pipe for the opticalintegrator, and a fly-eye mirror that includes reflective opticalelements for the optical integrator.

[0091] The present invention can provide an exposure apparatus thatprevents shielding of the illumination light and has excellent imagingperformance.

[0092] In addition, the present invention can provide an exposureapparatus that minimizes changes in performance (such as efficiency)other than the telecentricity when the telecentricity of theillumination ray shape (or an effective light source shape) iscorrected, and has excellent imaging performance.

What is claimed is:
 1. An exposure apparatus comprising: an illuminationoptical system for illuminating a reticle using light from a lightsource, wherein said illumination optical system includes an opticalintegrator for forming a secondary light source from the light, and avariable stop arranged at or near a position where the secondary lightsource is formed, the variable stop being configured to vary an aperturediameter that defines a numerical aperture of said illumination opticalsystem; a projection optical system for projecting a pattern on thereticle onto an object to be exposed, wherein said projection opticalsystem includes an aperture stop arranged at a position substantiallyoptically conjugate with the variable stop, said aperture stop defininga numerical aperture of said projection optical system; and a controllerfor controlling the aperture diameter of the variable stop in saidillumination optical system as the aperture diameter of the variablestop varies so that an image of the secondary light source formed at ornear the aperture stop can fall within the aperture diameter of theaperture stop.
 2. An exposure apparatus according to claim 1, whereinthe image of the secondary light source has a center part and aperipheral part that is darker than the center part.
 3. An exposureapparatus according to claim 1, wherein said optical integrator includesplural optical elements, and wherein said controller controls theaperture diameter of the variable stop in said illumination opticalsystem so that σ is equal to or smaller than (x−1)/x where x is thenumber of the optical elements corresponding to σ=1.
 4. An exposureapparatus according to claim 1, wherein said controller controls so thata ratio of the numerical aperture in said illumination optical system tothe numerical aperture in said projection optical system is equal to orsmaller than 0.95.
 5. An exposure apparatus according to claim 1,wherein said illumination optical system further includes: a zoomingoptical system for introducing the light to the optical integrator, andfor adjusting a size of the secondary light source; and a condenseroptical system that introduces the light from the optical integrator tothe reticle, and includes at least two or more optical elements, whereinthe zooming optical system adjusts the size of the secondary lightsource in accordance with an adjustment of an interval between theoptical elements that constitute the condenser optical system.
 6. Anexposure apparatus according to claim 5, wherein the adjustment of theinterval between the optical elements is used to adjust telecentricityfor the light to expose the object.
 7. An exposure apparatus accordingto claim 5, wherein the condenser optical system has at least two groupsof optical systems, and makes a focal length and a back principal pointposition of the condenser optical system substantially constant, whilemaking a front principal point position of the condenser optical systemvariable.
 8. An illumination apparatus for illuminating a surface usinglight from a light source, said illumination apparatus comprising: acondenser optical system that includes at least two groups of opticalsystems for introducing the light into the surface, wherein saidcondenser optical system makes a focal length and a back principal pointposition of the condenser optical system substantially constant, whilemaking a front principal point position of the condenser optical systemvariable.
 9. An illumination apparatus according to claim 8, wherein anadjustment of the front principal point position is used to adjusttelecentricity for the light to illuminate the surface.
 10. Anillumination apparatus according to claim 8, further comprising anadjuster for varying the front principal point position of the condenseroptical system while making the focal length of each of the condenseroptical system and the back principal point position substantiallyconstant.
 11. An illumination apparatus for illuminating a surface usinglight from a light source, said illumination apparatus comprising: anoptical integrator for forming a secondary light source from the light;and a condenser optical system that introduces the light from saidoptical integrator into the surface, and includes at least two groups ofoptical systems, wherein said condenser optical system makes a focallength and a back principal point position of the condenser opticalsystem substantially constant, while making a front principal pointposition of the condenser optical system variable.
 12. An illuminationapparatus according to claim 11, wherein an adjustment of the frontprincipal point position is used to adjust telecentricity for the lightto illuminate the surface.
 13. An illumination apparatus according toclaim 11, further comprising an adjuster for varying the front principalpoint position of the condenser optical system while making the focallength of each of the condenser optical system and the back principalpoint position substantially constant.
 14. An illumination apparatusaccording to claim 11, wherein said condenser optical system can move animage of the secondary light source in an optical-axis direction, whichimage is formed at a position substantially optically conjugate with aposition where the secondary light source is formed.
 15. An illuminationapparatus for illuminating a surface using light from a light source,said illumination apparatus comprising: a zooming optical system forintroducing the light to an optical integrator and for adjusting a sizeof a secondary light source formed by the optical integrator; and acondenser optical system that introduces the light from the opticalintegrator to the surface to be illuminated, and includes at least twoor more optical elements, wherein said zooming optical system adjuststhe size of the secondary light source in accordance with an adjustmentof an interval between the optical elements that constitute thecondenser optical system.
 16. An exposure apparatus comprising: anillumination optical system according to claim 8; and a projectionoptical system for projecting a pattern on a reticle illuminated by saidillumination optical system, onto an object to be exposed.
 17. Anexposure apparatus comprising: an illumination optical system accordingto claim 11; and a projection optical system for projecting a pattern ona reticle illuminated by said illumination optical system, onto anobject to be exposed.
 18. An exposure apparatus comprising: anillumination optical system according to claim 15; and a projectionoptical system for projecting a pattern on a reticle illuminated by saidillumination optical system, onto an object to be exposed.
 19. A devicefabricating method comprising the steps of: exposing an object using anexposure apparatus according to claim 1; and developing the object thathas been exposed.
 20. A device fabricating method comprising the stepsof: exposing an object using an exposure apparatus according to claim16; and developing the object that has been exposed.
 21. A devicefabricating method comprising the steps of: exposing an object using anexposure apparatus according to claim 17; and developing the object thathas been exposed.
 22. A device fabricating method comprising the stepsof: exposing an object using an exposure apparatus according to claim18; and developing the object that has been exposed.